Pneumatic power control



-Aug.2,1938. I H- 2,125,601

PNEUMATIC POWER CONTROL Filed Feb. 2, 1937 2 Shets-Sheet 1 a. 2, 13. HBUSCH 2,115,@1

I PNEUMATIC POWER CONTROL Filed Feb. 2, 1957 2 sheets-sheet 2 3 w Ki R m0,; U Q q Q r 9 Q Q n a a J N w i m & a

x mm A u} a n A m 1 K\ x Q m w Patented Aug. 2, 1938 omrso STATES2,125,601 PNEUMATIC POWER CONTROL Herman Busch, Long Island City, N. Y.,assignor to Airmatic Systems, Inc., New York, N. Y., a corporation ofNewYork Application February 2, 1937, Serial No. 123,672

12 Claims.

This invention relates to power or motive fluid controllers forpneumatic conveyor systems and more particularly to the general type ofcontrollers, the purpose of which is to reduce the to- 15 tal amount ofmotive fluid or power required to operate such systems. An early priorart controller of this type is disclosed in Patent No.

968,576 granted to Libby on August 30, 1910.

In the Libby type of controller a main motive fluid Valve opens for aperiod during which transmission is accomplished and closes at the endof the period, remaining closed until transmission is again desired.During this period of no transmission a so called minimum flow of fluidis maintained in the transmission line by means such as a by-pass aroundthe main valve. For accomplishing the opening of the valve at thebeginning of a transmission period pneumatic means designed to respondto pressure changes in the transmission line opens a port to admitoperating fluid to a motor which in turn opens the main valve. When themain valve reaches full open position the pressure responding means isrendered inoperative, whereupon the main valve closes by movement over atime interval determined by leakage of the operating fluid from themotor. As the main valve reaches closed position the response means isreconditioned or restored for the next transmission cycle.

The primary object of this invention is to provide an improved form ofpower control for carrying out an operative cycle similar to the Libbyvalve but with simplified mechanism operating in a smoother and morepositive manner.

Although Libby hasbeen widely acknowledged as having disclosed the basicprinciples of the type of power controller for pneumatic systems knownas the minimum flow type, the Libby valve has never'been widely used.

Another object of this invention is to overcome some of the difflcultiesexperienced with the Libby valve by equalizing the pressures in thepressure response or control pneumatic at the end of the opening strokeof the main valve at atmospheric pressure instead of at sub-atmosphericpressure.

Another object is to provide a positive and accurate pilot vent valveoperation so that a more sensitive and accurate balance on the responsediaphragm becomes practical.

Another object is to provide a power control apparatus employing apneumatically operated control valve which, with its operatingdiaphragm, is biased toward closed position and responsive to thepresence of a carrier in the transmission line to open the valve againstthe bias and means operative by the movement of the main valve at theend of its opening stroke for equalizing the pressures on the oppositesides of the diaphragm by the displacement of line pressure on theresponse side of the diaphragm with atmospheric pressure for permittingthe valve to close under action of the bias means.

Another object is to arrange the atmospheric and transmission line portsclose together so that they may be located'remotely from the responsepneumatic and communicate therewith through a single passageway. v

A further object is to provide a single passageway for connecting theclosed chamber of the response pneumatic to the atmospheric andtransmission line ports.

A still further object is to provide a simplified form of means forconditioning or controlling the action of the auxiliary or responsepneumatic.

Still another object is to provide an improved form of quick closingvalve.

These and other objects will be apparent from the following descriptiontaken in connection with the accompanying drawings in which:

Fig. l is a diagrammatic View of asingle conveyor line including acontrol mechanism;

Fig. 2 is a'sectional view showing the parts when the main valve is inclosed position;

Fig. 3 is a sectional view showing the parts in the position they assumewhen the main valve is in full open position;

Fig. 4 is a fragmentary view of a modification of the invention withparts in normal position, similar to Fig. 2; and,

chamberswith means for connecting the diaphragm to structure to beoperated thereby or a motor performing the equivalent functions.

Referring now to Fig. 1 of the drawings, that portion of a pneumaticcarrier system pertaining to a single conveyor line is diagrammaticallyil- Fig. 5 is a detail view of the quick closing valve lustrated. From acentral station desk l6 dispatch lines extend out to varioussub-stations. A single line employing a control device comprises asending tube having a dispatch terminal I2 and a return tube l3 providedwith the usual delivery terminal I4. From the latter terminal anextension tube |5 passes down through the central desk I!) and connectswith the power control device IS. A suction tube I1 connects with theusual suction or header l8 in which a vacuum is continuously maintainedby means of a suitable exhauster, not shown. In other words, theexhauster is the common power source and the device-Hi controls thepower expended in a single line. A continuous air passage or conduit isformed by the parts enumerated from the dispatch terminal |2 through thedispatch and return tubes and I3 and the controller l6 to the exhauster.

Referring to Figs. 2 and 3, the controller |6 comprises a casing 2|divided by a septum 22 into two chambers, 23 and 24. Chamber 23 is incommunication with the transmission line and chamber 24 is incommunication with the suction line. The septum 22 is provided with twoports, a large port 25 which is controlled by a main valve 26 and asmall port 21 which is controlled by an auxiliary valve 28. Theauxiliary valve is opened by a screw threaded stem 29 and is setnormally off its seat to provide a small air passage through which ismaintained a continuous stream of air flowing from the transmissionline. This continuous flow of air will be hereinafter referred to as theminimum flow.

A motor 30 enclosed in a housing 3| is provided at the side of casing 2|for operating the main valve 26. This motor is comprised of diaphragm 32connected to the main valve by means of a stem 33 which reciprocatesthrough a bearing 34 in the inner wall of the motor housing. The housing3| comprises a saucer shaped base section 35 and a similar shaped cap 36attached to the base with the rim of the diaphragm 32 held between thesetwo elements.

The diaphragm divides the housing into inner and outer chambers 31 and38. The inner chamber 31 communicates freely with the suction or lowpressure chamber 24 through a relatively large unrestricted opening 39.The chamber 38 communicates with chamber 31 through a restricted port 4|and a valved port 42, hereinafter more fully described. The size of theopening of port 4| is regulated by needle valve 43. This portconstitutes a continuous leakage connection between chambers 31 and 38by means of which the closing time of the main valve is determined aswill hereinafter appear.

As already indicated the stem 33 extends through the main valve 26. Atits outer end the stem is carried in the central opening of a bossmember 44 disposed at what is the rear of the structure viewed as it isordinarily installed in service. This boss, as will presently bedescribed, carries a pilot valve which is employed to introduceatmospheric pressure into and out it off from the closed chamber of thecontrol pneumatic to condition it for proper sequence of operation. Theinner face of boss 44 carries a recess 45 in which is seated the outerend of compression spring 46. The inner end of the spring is secured tostem 33 and exerts a force suiiicient to hold valve 26 normally on itsseat.

The central opening 41 of boss 44 forms a bearing for the outer end ofstem 33 and extends through a sleeve 48 formed at the outer face of theboss. A plate 5| is mounted to reciprocate upon this sleeve. The outerend of the stem 33 is turned down to a smaller diameter to form shoulder52 thereupon. When the stem moves to its extreme left position, theshoulder 52 moves outwardly beyond the end of sleeve 48 a short distanceas shown in Fig. 3. In valves constructed according to this inventionfor experimental use the shoulder moves out a distance of about A; of aninch or less. At the outer face of plate 5| a disc 53 surrounds thereduced portion of the stem. Normally this disc is positioned at theouter end of sleeve 48. When the stem moves outwardly the disc isengaged by shoulder 52 moving plate 5| out a distance corresponding tothe protrusion of the shoulder. The outer end of the stem extends beyonddisc'53 and carries an adjustable collar 54. This collar is set so thatwhen the main valve 26 is moved to its seat the plate 5| is broughtagainst the face of the boss 44. It will be noted that shoulder 52 andcollar 53 form a lost motion connection between the stem and plate 5|. Aspring pressed plunger 56 set in one side of plate 5| bears upon sleeve48 to form a friction bearing for the plate to limit its movement tothat imparted to it by stem 33 through the lost motion connection.

The valve opening movement of motor 3| is determined by a control valve6| disposed to normally close a passage 62 leading from atmospherethrough valve seat 63 to chamber 38. This control valve may be biasedtoward closed position either by gravity, as shown, or by a loadingspring or both. The valve is lifted by auxiliary motor 64 and the biaseffects reclosing when the lifting force of the motor is removed. Thismotor comprises a casing which is divided into two chambers 65 and 66 bymeans of a smalldiaphragm 61, the latter being connected through asuitable operating stem to valve 6|. In the gravity biased form shown,the amount of bias is changed or regulated by exchanging washers ofdifferent weights at the upper end of the stem of the valve 6 Thisprovides adjustment and at the same time enables the retention of thedesirable characteristic of gravity bias which makes for extremelysensitive operation.

The lower chamber 66 is continuously open to the atmosphere throughports 68. The upper chamber 65 has a passage leading therefrom throughtube 12 which passes through the valve housing 2| and forms a nipple 73at the back. The passage continues from this nipple through a flexibletube 14 such as rubber and through nipple 15 to a recess 16 provided inboss 44.

Recess 16 is provided with two ports, port I! constantly open to chamber23 carrying transmission line pressure and valved port 18 normallyclosed by plate 5| but when open admitting atmosphere to the recess.Port 78 is made large in relation to port l1 so that when the formerport is opened, air passing through port ll to the vacuum space will beineffectual to maintain a reduced pressure in the recess 76. While port11 is shown to be smaller than the passageway H the size of the openingdoes not impose any appreciable restriction upon the speed with which achange in pressure in chamber 23 will be transmitted through thepassageway TI to chamber 65 when the atmospheric port 18 is opened orclosed. The response of diaphragm 67 is always substantiallyinstantaneous to any change in pressure sufficient to move it. Thepurpose of the proportion or relation of size of the ports 1'! and 18 ismerely that port 1'? shall be effectively restricted only with respectto atmospheric port 18. The.

use of chamber 16 located in the boss 44 enables the ports'l'l and 18 tobe located close together so that they may communicate with thediaphragm chamber 65 by a singlepassageway. In

addition this also facilitates the arrangement for controlling bothports by valves as shown in Fig. 4 and later to be described. 7

The port 18 is preferably faced with a soft resilient ring 19 which maybe live rubber or the like. This ring is preferably of sufiicientthickness to be slightly compressed when plate is brought intoengagement with the face of the boss'44 as the main valve reachesclosedposition.

With plate 5| acting as the valve and the ring 19 acting as the valveseat the pilot valve, already referred to, is formed and acts to openand close port 18in accordance with the position given plate 5| by themovement of valve stem 33 as the valve opens and closes. The pilot valvethus formed will hereinafter be referred to as pilot valve 89.

It is now desired to point out some of the particular advantages of theform of pilot valve and its manner of operation. In the first place, thepilot valve is opened and closed by movement in a plane perpendicular toits seat. In other words, it is a poppet valve type of movement, openingalong the entire perimeter of its seat. This means that considerableflow area can be opened up with a relatively small movement of the valvedisc 5|. Another feature is that the valve is large in proportion to theflow through it. These two features combined make it possible toaccomplish effective pilot valve action with a small movement of plate5|. With only a small movement required it has been found feasibleaccording to this invention to use a direct lost motion connection withthe main valve for movement in both directions so that the pilot valveis moved with the main valve for a small part of its stroke at the endof its movement.

With this arrangement, by the time the pilot valve is sufficientlyclosed for the transmission line pressure to begin to become establishedin control diaphragm chamber 65 the main valve will sufficiently closeto reduce the flow to substantially minimum flow. This enables theweight of the assembly of the control diaphragm 81 and control valve 5|to be adjusted to respond to a pressure only slightly below minimum flowpressure providing a very sensitive control. This in turn makespractical a very low minimum flow with a maximum saving of power.

It has been found that this type of pilot valve arrangement provideseffective control without the use of the quick closing arrangement laterto be described. Nevertheless, the quick closing of the main valveenables the pilot valve to function with increased effectiveness. On theother hand, as it will hereinafter appear, the primary advantage of thequick closing feature is to cut down the period of flow restriction dueto the closing of the main valve under conditions in which the valvemust reopen to complete the transportation of the carrier or carriers inthe line.

Fig. 4 shows a modified form of boss structure providing for a valvecontrolled transmission line port as well as a Valve controlledatmospheric port. In this form the port H is enlarged. to receive abushing 8|. This bushing is provided with a central opening to receivestem 82 of a valve 83 and one or more other openings 84 acting as portsor passages through the bushing.

The valve 83 is arranged to seat upon the outer end of the bushing so asto close the passages 84 and is carried to its seat as plate 5|approaches its outward position by a leaf spring 85 secured to a boss 86and having its outer end bearing upon the head of the valve. It isopenedby the valve stem 82 being ofsuch alength as to engage the face of plate5| and carry the valve 83 off its seat a short distance when the platecomes to its normal position of rest upon the face of the boss 44.

With this arrangement the atmospheric port will be closed while thetransmission line port is open and vice versa. In other words, in theirnormal position, with the main valve closed, the atmospheric port 18 isclosed while the transmission line ports 84 are open. Then when the mainvalve moves outward to open position and the shoulder 52 moves the plate5| outward, ports 84 are closed as port 18 opens.

The advantage of this modified form will more fully appear in thedescription of the operation .but may brieflybe stated as follows:First, there is no air intake through the transmission line ports orpassages 84 while the vent valve 89 including port 18 is open. Thisamong other things lessens the likelihood of the accumulation of lintand dust in the passages which might restrict the air flow th'erealong.A second advantage is that the flow area through the passages in bushing8| may be increased beyond the strict relation to atmospheric 'port '58required in the other form, thus making dust accumulations in thepassages less serious.

Another feature of this invention is the auxiliary leak orquick closingvalve 42 controlling a passage through the diaphragm 82 constituting anauxiliary connection between the chambers 31 and 38. This passage isprovided by an outer'bushing 88 arranged to pass through the diaphragm32. This carries an inner bushing 89 which is similar-in construction tobushing 8| shown in Fig. 4. One or more passages 9| pro vide the flowarea through the bushing while the stem 92 of valve 93 passes through acontrol opening in the bushing. In closed position the valve 93 seatsover the outer end of passage 9|. The outer'end of the valve stem 92 isprovided with a head 94 and a compression spring 95 surrounding the stemof the valve and resting against the head to normally hold the valveclosed.

Fig. 2 illustrates the position of the leak valve when the main'valve 26is closed. In this posiare engaged by the conical portion ||l| of thebushing 88 they will move outwardly to trip the auxiliary valve closedby separating the perches sufficiently to permit the head 94 of thevalve stem to pass through. The point of tripping is regulated by screwI92. The sequence of the operation of the various parts of the leakvalve just described will be set forth in detail in the generaldescription of operation to follow.

Assuming the parts to be in their normal or non-operated position asshown in Fig. 2 the and begins its closing movement.

operation of the control valve may be described substantially asfollows:

The main valve is closed, the control valve 6| closed, the pilot valveclosed, the auxiliary lead valve 42 closed and'the minimum flow valve 28adjusted slightly open. The drag or friction of the slight or minimumflow of air through the line reduces the pressure in the end of the lineadjacent to the control valve to a sub-atmospheric pressure. In practicethe amount of minimum flow is determined by first opening valve 28 untilthe drag of the minimum flow air is sufficient to lift the controldiaphragm 61 and valve 6| off its seat with the main valve closed, thenby closing the minimum flow off until the control diaphragm and valveremain down after each operating cycle until a carrier is introduced.

With this adjustment made, upon the introduction of a carrier in theline the minimum flow of air will be blocked off and the air ahead ofthe carrier exhausted through the minimum flow port. This causes in theline a reduction in pressure which is transmitted from chamber 23through port 11, recess 16 and passage H to chamber 65 raising diaphragm61, lifting valve 6| and admitting atmospheric air through passage 62 tochamber 38. Chamber 3! being at the reduced pressure or vacuum of theexhaust line, diaphragm 32 is drawn inwardly as atmosphere enterschamber 38.

As the diaphragm begins to move it carries the parts including stem 33,main valve 26, collar 54, and auxiliary leak valve stem 92 to the left.In its outward movement valve stem head 94 will engage the back slopedsurfaces of perches 98 springing them apart as it passes through.

As the valve stem approaches the end of its leftward or opening strokethe shoulder 52 engages collar 53 and begins to move the plate 5| awayfrom the face of boss 44. As soon as the plate has moved away a distancewhich will permit more atmospheric air to enter port 18 than is beingwithdrawn through port 11, atmospheric pressure will be established inrecess 16 and through communicating passage H in chamber 65 also.

As soon as chamber 65 reaches substantially atmospheric pressure, thelower chamber 66 being constantly at atmospheric pressure, the pressureson opposite sides of diaphragm 61 are equalized permitting the gravitybias on the diaphragm and valve 6! to close the latter. As soon as valve6| is closed stem 33 ceases its opening movement Plate 5| is held in itsoutward position by the frictional engagement of spring pressed pin 56with sleeve 49.

The time of the closing movement of the initial portion of the closingstroke is determined by the setting of the leakage screw 43. The valvewill continue its closing movement at this rate until the head 94 of thestem of the auxiliary leak valve 42 engages the trip perches 98. At thispoint the travel of the stem 92 and the member 93 in the direction ofdiaphragm 32 ceases and the valve 42 is opened by the continued movementof the diaphragm. This opens the auxiliary leak port 9! suddenlyincreasing the leakage rate or the rate of the pressure equalizationbetween chambers 31 and 38. With the additional leak thus provided, themain valve will travel with a quick movement to the end of its stroke.Just before the main valve reaches the end of its stroke the conicalsection IBI of the auxiliary valve housing engages the flared portions99, spreading apart perches 98 and permitting the head 94 urged byspring 95 to drop through, closing the auxiliary leak valve. The pointin the main valve closing stroke at which the auxiliary leak valvebegins to open is determined by the length of the stem 92 as adjusted bythelock nuts behind the valve. The point at which the auxiliary leakvalve is tripped closed is determined by the setting of the screw 502which adjusts the trip member 9'! inwardly and outwardly so that theconical section Illl engages it earlier or later in the stroke.

In addition to the above functions performed as the main valve 26approaches the end of its closing stroke pilot valve 80 is closed bycollar 54 engaging disc 53 on plate 5| and carrying them to the rightuntil the face of the plate covers port 18. This does not take placeuntil the main valve practically becomes seated. The closing time of thevalve is set so that under normal conditions the carrier will havecompleted its travel through the line and will have been discharged bythe time the valve has closed. Therefore, the line being open, thepressure in chamber 23 will have substantially reached the minimum flowpressure. As the pilot valve closes, this minimum flow pressure istransmitted to chamber 65. However, since diaphragm 61 responds only topressures below minimum flow it will remain seated. On the other hand,if due to some abnormal condition the carrier has not been discharged,the pressure on the transmission line side of the valve in chamber 23will not reach the minimum flow pressure andthe diagram 61 will beraised as soon as the pilot valve is closed, immediately initiating thereopening of the main valve, whereupon it will follow through anotherclosing cycle.

It is to be noted that since the auxiliary leak valve 42 is alwaysclosed. at the end of the closing stroke of the main valve the openingresponse of the main valve will be of the same character as though theauxiliary leak valve were not employed. In other words, if the type ofleak valve which, according to this invention, is tripped closed at theend of the closing stroke of the main valve were not used, at thebeginning of the opening stroke both the auxiliary leak port and themain leak port would be open and air would escape through both of theseports at substantially the same rate as that at which it escaped tocause the quick closing. This must necessarily be a considerable flow,easily sufiicient to cause the opening action of the main diaphragm tobe sluggish without the use of a relatively large atmospheric flowpassage 62 necessitating a correspondingly large valve 6|. This isundesirable because the valve 6| when seated is being drawn toward itsseat by the reduced pressure below the seat and a large atmospheric portvalve entails considerable difficulties in producing sensitive operatingmeans for opening the valve. Therefore, the employment of a quickclosing or auxiliary leak valve such as disclosed in this inventionwhich does not effect the opening stroke of the main diaphragm providesa highly desirable type of valve operation.

The operation of the modified form of structure for valve-closing boththe atmospheric and transmission line ports entering recess 76 as shownin Fig. 4 will now be described. When the controller is provided withthe form of structure shown in Fig. 4, the other parts of the mechanismoperate in substantially the same manner as in the form shown in Figs. 2and 3. The parts of the modified form illustrated in Fig. 4 also operatein substantially the same manner except that then the plate 51 is movedoutwardly at the end of the opening stroke of the main valve to open thepilot port 18, the valve 83 moves simultaneously to the left under theinfluence of spring 85 until the valve is seated over the inner end ofthe transmission line passages 84; the length of the valve stem 82 beingsuch as to permit valve 83 to become seated at or before the end of theoutward movement of the plate 59. Another differentiation is that Whilethe main valve is closing and until the plate 5! is engaged by collar54, the passages 84 remain closed and no air is being drawn through thetransmission line ports during this time. As the plate M is moved backto its normalposition closing port '58, the stem 82 of the valve 33 isengaged by the face of the plate 5! and moved to the right again openingthe passages 84.

It will be seen, therefore, that with this form only a relatively smallamount of air is drawn through the transmission line ports or passagesand therefore the likelihood of these passages becoming clogged withlint and dust is considerably reduced. In addition, as already pointedout, the employment of a valve for the'transmission line port as Well asfor the atmospheric port makes it unnecessary to make the transmissionline port smaller than the atmospheric 'port as in the other form.

From the above description it will be seen that an improved form ofpower control mechanism constructed according to this invention has beenprovided employing the basic principles of the Libby type of valveembodied in an extremely simple form of mechanism arranged forconvenient adjustment and effective operation. In addition the form ofstructure here employed overcomes many of the difficulties inherent inthe Libby structure giving a controller which will operate effectivelyover long periods of time with the minimum of adjustment and repair. Itis to be understood that this invention may be embodied in many otherforms of apparatus and it is desired, therefore, that only suchlimitations shall be placed thereon as are imposed by the prior art orby the claims appended hereto.

What I claim is:

1. Power control apparatus for a pneumatic conveyor having atransmission line, an exhaust line and a casing therebetween enclosing amain valve for controlling the line fluid flow, means for opening andclosing the main valve, means for establishing a minimum flow of airthrough the line when the main valve is closed, and means forcontrolling the opening and closing of the main valve in response to theintroduction of a carrier in the line, said controlling means includinga control diaphragm normally responsive to said carrier introduction, arecess in said casing disposed remotely from said diaphragm and a singlepassageway establishing communication between said recess and saiddiaphragm, said recess being provided with two ports, one of said portsleading to the transmission line, the other port to the atmosphere,valve means for the atmospheric port, said valve means being normallyclosed for rendering said diaphragm normally responsive to theintroduction of a carrier in the line and movable to open position forrendering the diaphragm unresponsive, and means operated by the movementof the main valve at the end of its opening and closing strokes foropening and closing said atmospheric port.

2. Power control apparatus for a pneumatic conveyor having atransmission line, an exhaust line and a casing therebetween enclosing amain valve for controlling the line fluid flow, means for opening andclosing the main valve, means for establishing a minimum flow of airthrough the line when the main valve is closed, and means forcontrolling the opening and closing of the main valve in response to theintroduction of a carrier in the line, said controlling means includinga control diaphragm normally responsive to said carrier introduction,constantly exposed on one side to atmospheric pressure and in apredetermined position withreference to said casing, a recess in saidcasing disposed remotely from said diaphragm and. communicating with theunexposed side thereof through a single passageway, two ports in saidrecess, one of said ports leading to the transmission line, the otherport being of a size suitable for quickly transferring atmosphericpressure to the diaphragm and leading to the atmosphere, the atmosphericport being sufiiciently larger than the transmission port to establishatmospheric pressure in the recess when it is open, and valve meansoperated by the movement of the main valve at the end of its opening andclosing stroke for opening and closing the atmospheric port.

3. Power control apparatus for a pneumatic conveyor having atransmission line, an exhaust line and a casing therebetween enclosing amain valve for controlling the line fluid fiow, means for establishing aminimum flow of air through the line when the main valve is closed, andmeans for controllingthe opening and closing of the main valve inresponse to the introduction of a carrier in the line, said controllingmeans including a control diaphragm normally responsive to said carrierintroduction, constantly exposed on one side to atmospheric pressure andassociated with said casing, a recess in said casing disposed remotelyfrom said diaphragm, a passage leading directly from said recess to thetransmission line, said recess normally having transmission linepressure therein, and means operated by the movement of the main valveas it approaches the end of its opening stroke for establishingatmospheric pressure in said recess and similarly operated at the end ofthe closing stroke of the main valve for'reestablishing transmissionline pressure and a single passageway for communicating the pressuresobtaining in said recess to the unexposed side of said diaphragm.

4. Power control apparatus for a pneumatic conveyor having atransmission line, an exhaust line and a casing therebetween enclosing amain valve for controlling the line fluid flow, means for opening andclosing the main valve, means for establishing a minimum flow of airthrough the line when the main valve is closed, and means forcontrolling the opening and closing of the main valve in response to theintroduction of a carrier in the line, said controlling means includinga diaphragm normally sensitive to transmission line pressure, saiddiaphragm being constantly exposed on one side to atmospheric pressure,means forming a chamber at the other side including the diaphragm as awall thereof, means providing a first and a second port communicatingwith said chamber, said first port means opening to the transmissionline, said second port means opening to the atmosphere, alternatelyseated valves for closing and opening said port means, the valve for thefirst port means being normally open and the othernormally closed forsensitizing the diaphragm, and means operated by the movement of themain valve as it approaches the end of its opening stroke for moving theport valves to close the first port and open the second fordesensitizing said diaphragm, and as the main valve approaches the endof its closing stroke for reversing the closing action of the valves forresensitizing said diaphragm.

5. In a power control apparatus for a pneumatic conveyor line, a valvefor controlling the flow of motive fluid in the line, resilient meanstending to close said valve, a fluid motor arranged so that when fluidis admitted thereto the motor moves to open said valve, means forclosing the valve including means for leaking out the admitted fluid ata predetermined rate for a part of the closing stroke, means forautomatically increasing said leakage rate as the valve approaches theend of its closing stroke, and means for restoring the leakage means toits condition of minimum leakage as the valve reaches the end of itsclosing stroke.

6. A pneumatic motor for use in pneumatic conveyor systems comprising ahousing having a motive fluid chamber therein, a diaphragm forming onewall of the chamber arranged to make forward and return strokes, a pairof leak ports for discharging the motive fluid from said chamber uponthe return stroke, one of said ports being continuously open, means foropening the other port during the latter part of the return stroke, andmeans for closing the same again at the end of the return stroke.

7. In combination, a main valve for controlling the flow of motive fluidthrough a pneumatic conveyor line or the like, a resilient means tendingto hold said valve closed, a fluid motor arranged to open the valveagainst the action of said resilient means, said motor comprising ahousing embodying a motive fluid chamber having a movable side wall andmeans for operatively connecting said wall and the valve, a controlledinlet port for admitting motive fluid to said chamber for opening thevalve, a continuously open regulatable leak port for bleeding the motivefluid out of said chamber at a determined rate for permitting the valveto close, a supplementary leak port through said movable wall, a valvehousing carried by said wall and including said supplementary port and aspring closed leak valve therefor, a stem for said valve extending inthe direction of the travel of said wall as the main valve closes, amovable perch arranged to intercept said stem as the wall approaches theend of its inward stroke for opening said supplementary leak port, andmeans for tripping out said perch at the end of the closing stroke topermit said valve to close.

8. A pneumatic motor for use in pneumatic conveyor systems comprising ahousing having a motive fluid chamber therein, a diaphragm forming onewall of the chamber arranged to make forward and return strokes, a pairof leak ports .for discharging the motive fluid from said chamber uponthe return stroke, one of said ports being continuously open, means foropening the other port during the latter part of the return stroke,means for closing the same again at substantially the end of the returnstroke and means for adjusting the point at which said reclosure occurs.

9. In a power control apparatus for a pneumatic conveyor having atransmission line, an exhaust line, and a casing therebetween enclosinga main valve for controlling the line air flow, means for establishing aminimum flow of air through the line when the main valve is closed,means for opening the main valve in response to the presence of acarrier in the transmission line,

and time controlled means for closing the valve, said response meansincluding a main pneumatic for moving the main valve and an auxiliarycontrol pneumatic for initiating the opening and closing strokes of themain pneumatic, said auxiliary pneumatic being sensitizable to thepresence of a carrier in the transmission line by having a diaphragmconstantly exposed on one side to atmospheric pressure, and having achamber at the other side provided with a passageway leading therefrom,said passage having a first port communicating with atmosphere and asecond port communicating with the transmission line, a valve for theatmospheric port normally closed for establishing transmission linepressure at said other side of the auxiliary diaphragm to sensitize thesame, means operable by the movement of the main valve at the end of itsopening stroke for opening said atmospheric valve for establishingatmospheric pressure in said chamber for desensitizing said diaphragmand at the end of the closing stroke for closing said atmospheric valvefor resensitizing said diaphragm, a valve for the transmission lineport, and means for operating it in conjunction with the atmosphericvalve for closing the transmission line port while the atmospheric portis open for segregating the transmission line pressure from saidpassageway while the atmospheric port is open.

10. Power control apparatus of the minimum flow type for a pneumaticconveyor line having a transmission tube and an exhaust tube and a mainvalve between said tubes for controlling carrier propelling air flowthrough the line, means for establishing a minimum flow of air throughthe line when the main valve is closed, a main pneumatic for operatingthe main valve and an auxiliary pneumatic responsive to the introductionof a carrier into the line for initiating the operation of the mainpneumatic and means for conditioning the response pneumatic including acontinuously open passage communicating from the latter to thetransmission line and a valve controlled atmospheric port along saidpassage, and means for operating said valve from the main valve.

11. Power control apparatus of the minimum flow type for a pneumaticconveyor line having a transmission tube and an exhaust tube and a mainvalve between said tubes for controlling carrier propelling air flowthrough the line, means for establishing a minimum flow of air throughthe line when the main valve is closed, a main pneumatic for operatingthe main valve and an auxiliary pneumatic responsive to the introductionof a carrier into the line for initiating the operation of the mainpneumatic and means for conditioning the response pneumatic including acontinuously open passage communicating from the latter to thetransmission line and a valve controlled atmospheric port along saidpassage and means for operating said valve from the main valve includingmeans for opening said valve at the end of the opening stroke of themain valve and for closing it at the end of the closing stroke of themain valve.

12. In a power control apparatus for a pneumatic conveyor having atransmission line, an exhaust line, and a casing therebetween enclosinga main valve for controlling the line air flow, means for establishing aminimum flow of air through the line when the main valve is closed,means for opening the main valve in response to the presence of acarrier in the transmission line, and time controlled means for closingthe valve,

said response means including a main pneumatic for moving the main valveand an auxiliary control pneumatic for initiating the opening andclosing strokes of the main pneumatic, said auxiliary pneumatic beingsensitizable to the presence of a carrier in the transmission line byhaving a diaphragm continuously exposed on one side to a constantpressure, and. having a chamber at the other side provided with apassageway leading therefrom, said passageway having a first portcommunicating with said constant pressure and a second portcommunicating with the transmission line, a valve for the constantpressure port normally closed for establishing transmission linepressure at said other side of the auxiliary diaphragm to sensitize thesame, means operable by the movement of the main valve at the end of itsopening stroke for opening said constant pressure valve for establishingthe constant pressure in said chamber for desensitizing said diaphragmand at the end of the closing stroke for closing said constant pressurevalve for resensitizing said diaphragm, a valve for the transmissionline port, and means for operating it in conjunction with the constantpressure valve for closing the transmission line port while the constantpressure port is open for segregating the transmission line pressurefrom said passageway while the constant

